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arXiv 2105.03079gr-qc
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普通曲速引擎违反了零能量条件

Generic warp drives violate the null energy condition

Jessica Santiago, Sebastian Schuster, Matt Visser

摘要:

最近的三篇文章声称,至少在理论上,可以建立满足弱能量条件(WEC)的正能量曲速驱动器,或者至少可以最大限度地减少WEC违规。这些主张充其量是不完整的,因为所提出的论点只证明了一组时间型观察者的存在,即共同运动的欧拉观察者,他们看到的是“美好的”物理。虽然这些观察者可能看到正的能量密度,但WEC要求所有类时观察者看到正的能量密度。因此,我们应该重新考虑这个问题。更仔细的分析表明,情况实际上比宣传的要严峻得多--所有物理上合理的曲速驱动器都会违反零能量条件,因此也会自动违反WEC,以及强能量和主导能量条件。虽然曲速引擎确实是投机物理学的有趣例子,但至少在标准广义相对论的框架内,能量条件的违反是不可避免的。即使在修正引力中,物理上合理的翘曲驱动仍然会违反纯粹几何零收敛条件和类时收敛条件,这反过来又会对任何修正引力翘曲驱动施加非常强的约束。

英文摘要:

Three very recent articles have claimed that it is possible to, at least in theory, either set up positive energy warp drives satisfying the weak energy condition (WEC), or at the very least, to minimize the WEC violations. These claims are at best incomplete, since the arguments presented only demonstrate the existence of one set of timelike observers, the co-moving Eulerian observers, who see "nice" physics. While these observers might see a positive energy density, the WEC requires all timelike observers to see positive energy density. Therefore, one should revisit this issue. A more careful analysis shows that the situation is actually much grimmer than advertised -- all physically reasonable warp drives will violate the null energy condition, and so also automatically violate the WEC, and both the strong and dominant energy conditions. While warp drives are certainly interesting examples of speculative physics, the violation of the energy conditions, at least within the framework of standard general relativity, is unavoidable. Even in modified gravity, physically reasonable warp drives will still violate the purely geometrical null convergence condition and the timelike convergence condition which, in turn, will place very strong constraints on any modified-gravity warp drive.

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